"Play it by ear." "Gone to pot." "In like Flynn." The English language is full of phrases that we casually throw into conversations, often without any idea of what they really mean or how they originated. Take, for example, the phrase, "The Real McCoy." We use it when referring to something that's the real deal -- the genuine article. But just who was "the real McCoy?" Where did this phrase come from?

The name McCoy might immediately bring to mind the Hatfield and McCoy clans, who quarreled along the West Virginia-Kentucky border in the 19th century, but there's no absolutely no evidence linking the phrase's origin to this famous family feud. Depending on which account you believe, the "real McCoy" was a boxer, an inventor, a rumrunner or a Scottish clan leader. Here are just a few of the phrase's possible origins:

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In the late 1800s, American welterweight champion Norman Selby boxed under the name "Kid McCoy." Two stories about Selby give a possible explanation for the phrase. In the first story, Selby was challenged by a drunk in a bar, who questioned whether he was really the legendary fighter he claimed to be. In response, Selby socked the drunk, sending him sprawling to the floor. When the man got to his feet, he announced that he was convinced the man who'd hit him was "the real McCoy." In the other story, sportswriters gave Selby the moniker because he was accused of throwing so many fights that they never knew which Selby -- the true fighter or fight thrower -- would show up at boxing matches.

In 1871, a Canadian inventor named Elijah McCoy came up with a lubricating device for steam engine locomotives. The success of his invention inevitably spawned imitations, which may have led railroad purchasing agents to ask for "the real McCoy."

During Prohibition, Florida rumrunner Bill McCoy was known for selling the good stuff. In other words, he never watered down his booze (the way most bootleggers did back then) to increase product. When his customers wanted the best rum, they may have requested it by his name.

These are all great stories, but the real origin of the phrase most likely lies in the misspelling of a Scottish name. A few possible contenders include a popular Scottish actor, a bandit or the chief of a Scottish clan, all of whom shared the name MacKay.

Once it became popular, the phrase was quickly adopted to promote one of Scotland's most famous exports -- whiskey. A reference in the 1856 Scottish National Dictionary mentioned, "A drappie (drop) o' the real MacKay," which was possibly the first time the phrase appeared in print. Messrs A. & M. Mackay of Glasgow used the slogan, "the real McKay," to advertise their whiskey brand in 1870. Once the saying reached the U.S., it was changed to its current form --"the real McCoy," likely thanks to the famous men who shared the name.